Personality, dietary identity, mental and sleep health in vegans and vegetarians: A preliminary cross‐sectional study

Abstract Background and Aims Plant‐based diets have gained popularity over the past decade. However, research regarding mental and sleep health benefits of following plant‐based diets are conflicting. As there are associations between mental/sleep health and various personality traits, and personality may differ between individuals who follow different diets, in this preliminary study, we examined the associations between mental and sleep health and (i) personality and (ii) dietary identity in individuals who follow vegan and vegetarian diets. Methods Cross‐sectional data on sociodemographic, personality traits, dietarian identity, overall mental health, depression, anxiety, stress, and sleep quality were collected from 57 vegan/vegetarian participants between the ages of 18–40. Results After controlling for various sociodemographic and lifestyle factors, linear regression models revealed that (i) higher dietarian private regard was a significant predictor of better overall mental health, (ii) lower levels of extraversion and higher levels of empathy predicted depression, (iii) higher levels of neuroticism and empathy predicted anxiety, (iv) higher levels of neuroticism, dietarian centrality, and neuroticism × centrality predicted stress, (v) higher levels of conscientiousness, lower levels of dietarian centrality, but higher levels of personal motivation and dietary strictness, as well as conscientiousness × centrality, conscientiousness × personal motivation, and conscientiousness × strictness predicted better sleep quality. Conclusions These preliminary findings suggest that not only personality traits, but also dietary identity was indeed related to mental and sleep health in individuals who follow plant‐based diets.


| INTRODUCTION
Vegan and vegetarian diets have gained increased popularity over the past decade, and in the United Kingdom, an increased proportion of individuals report consuming plant-based dietary patterns. 1 While vegan and vegetarian diets are associated with positive health outcomes, including a lower body mass index (BMI), better cardiometabolic profile 2,3 and reduced risk of cardiovascular disease, 4 research evidence suggests that individuals may be at risk of suboptimal nutrition. 5 On the other hand, results in literature in relation to mental and sleep health are conflicting. While some investigations found positive results between vegan and/or vegetarian diets and mental and sleep health outcomes 6-8 others reported null or inverse associations. [7][8][9][10][11] Limitations may include inconsistencies in the definition of vegan and vegetarian diets, classification of meat products and processing 10 or different covariates included in the statistical models. An important consideration is that psychological and behavioral characteristics may differ between vegans, vegetarians, and omnivores, therefore, variation in personality and dietary identity factors may have an impact on the associations between diet, mental and sleep health.
Personality traits are found to vary with dietary status 12 and types of meat consumed, 13 such that higher scores of Openness, Conscientiousness, and Agreeableness are associated with lower meat consumption. Compared to omnivores, vegetarianism is associated with higher scores of Openness and Empathy 14,15 and higher levels scores of Openness and Agreeableness. 16 However, compared to omnivores, vegetarians were also found to score higher on neuroticism and depression. 17 Furthermore, systematic differences in psychological traits may exist between vegans and vegetarians. One study comparing vegans and vegetarians reported that neuroticism was marginally higher in vegetarians, yet no differences were found in the other four personality domains. 18 However, another study reported that vegans scored lower on neuroticism and higher on openness and empathy compared to vegetarians. 15 The variation in personality traits may be linked to mental and sleep health outcomes. Research has shown that neuroticism is strongly linked to internalizing psychopathologies such as depression and anxiety disorders. 19 Additionally, higher levels of neuroticism were found to be associated with affective disorders such as major depressive disorder and social anxiety 20 and higher levels of selfreported depression and anxiety 21 while higher scores of neuroticism, and lower scores of extraversion, conscientiousness, and agreeableness, predicted an increased risk for anxiety and depression. 22 Further longitudinal research indicates that high levels of neuroticism predict the risk for the development of anxiety and depressive disorders, 23 and another study reported that high neuroticism and low extraversion were found to predict the chronicity of diagnoses and symptoms of various affective disorders. 24 In addition to big five personality traits, meta-analytic evidence showed that affective empathy (but not cognitive empathy) trait was positively correlated with depression 25 and social anxiety. 26 In terms of sleep, personality traits, such as neuroticism, is also shown to be associated with sleep health. Higher neuroticism was found to be correlated with poor sleep, whereas higher extraversion, agreeableness, and conscientiousness were shown to be linked to better sleep outcomes. 27,28 In line with this, high neuroticism and low conscientiousness was shown to predict poor sleep (poor sleep hygiene, low sleep quality, and increased sleepiness). 29 Additionally, longitudinal evidence from four prospective studies has showed that high neuroticism and low extraversion were associated with worse sleep quality over time and low conscientiousness was associated with worsening of sleep quality over time. 30 Alongside personality traits, it has been proposed that veganism extends beyond the diet, but encompasses a set of beliefs, attitudes, and motivations to which the individual identifies, and identity may shape the way in which the individual behaves/thinks/feels and communicates with the world. 31 Accordingly, albeit limited, research has shown that vegetarians (compared to omnivores) adhered to their diets more strictly (higher strictness), felt stronger motivations to follow their diet (higher motivation), evaluated vegetarians more favorably (higher private regard), evaluated other individuals who follow other types of diets more negatively (lower out-group regard), and felt that vegetarians were judged more negatively by others (lower public regard). [32][33][34] On the other hand, omnivores evaluated individuals who follow other types of diets more positively (higher out-group regard) and did not feel judged negatively more by other people for their dietary choices (higher public regard). 32 Additionally, it has also been shown that vegetarians and vegans exhibit different dietarian identity profiles. For instance, it has been reported that vegans (compared to vegetarians) saw their diet as a fundamental part of their identity (higher centrality), had more positive feelings (lower out-group regard), and had stronger motivations to adhere to veganism (higher prosocial, personal, and moral motivations). 33,34 The observed variations in identity, attitudes, and motivations associated with veganism and vegetarianism could potentially impact mental and sleep health outcomes.
Taken together, differences in personality traits and dietary identity observed in individuals who follow a vegan and vegetarian diet suggests a potential link between these factors and mental and sleep health. To the best of our knowledge, irrespective of diet type, dietary identity in relation to mental and sleep health has not yet been examined. Given the associations reported above between (i) diet type and dietary identity, personality, and mental and sleep health, as well as (ii) personality, and mental and sleep health, we expect dietary identity to contribute to the complex relationships between personality and health. Hence, in the current study, our aim was to examine the roles of personality and dietary identity in predicting mental and sleep health-related outcomes in individuals who adhere to vegan and vegetarian diets.  Table 1. Inclusion criteria included healthy adults between ages of 18-40 years who follow a vegan or vegetarian diet. Exclusion criteria included: any history of, or taking medication for, psychiatric, sleep disorders, or neurological disorders.

| Measures
Participants were asked to state their age, sex, weight and height, education, employment, and household income. They were also asked to report their caffeine, alcohol, and cigarette consumption, as

| BFI
The BFI explores five personality dimensions: Extraversion, Agreeableness, Conscientiousness, Neuroticism, and Openness. 37 The scale consists of 44 questions measuring to what degree an individual identifies with each dimension; for example, "I see myself as someone who is talkative." The scale is measured on a five-point Likert scale, from one ("disagree strongly") to five ("agree strongly"), and higher scores indicate higher levels of extraversion, agreeableness, conscientiousness, neuroticism, and openness. The Cronbach α in the current study is 0.63.

| EQ-10
The EQ-10 consists of 10 questions exploring self-reported empathy 38 ; for example, "I am good at predicting how someone will feel," and participants are required to indicate to what degree they agree with each statement. The scale is scored on a four-point Likert scale, from one ("strongly agree") to four ("strongly disagree") and higher scores indicate higher levels of empathy.
No Cronbach α was calculated in view of the brevity of this measure.

| DASS
The DASS aims to measure three dimensions: depression, anxiety, and stress. 39 This scale consists of 42 questions, such as "I felt terrified," requiring participants to note how frequently they identified with this statement over the past week. DASS is scored on a four-point Likert scale, from zero ("did not apply to me at all") to three ("applied to me very much, or most of the time"). On the depression subscale, a score of 0-9 indicates no depression, 10

| WEMWBS
The WEMWBS is a 14-item scale, exploring how psychological functioning and positive affect, 40

| PSQI
The PSQI consists of 19 items assessing sleep quality and disturbances over the past month. 41 The scale is split into seven components, subjective sleep quality, sleep latency, sleep duration, habitual sleep efficiency, sleep disturbances, use of sleeping medication, and daytime dysfunction; for example, "over the last month, how often have you had trouble sleeping because you feel too hot." These components are scored individually, then summed to form a global score, determining whether a participant Is a "good sleeper" or "poor sleeper." Higher scores indicate worse sleep quality.
No Cronbach α was calculated in view of the brevity of this measure.

| DIQ
The DIQ consists of 34 total questions, split into nine subsections. 34 The first subsection contains only one question regarding food groups generally not eaten. The following 33 questions are split into subsections on centrality, private regard, public regard, out-group regard, prosocial motivation, personal motivation, moral motivation, and strictness. The scale is scored on a seven-point Likert scale from one ("strongly disagree") to seven ("strongly agree"), and higher scores indicate higher dietarian centrality, private regard, public regard, out-group regard, prosocial motivation, personal motivation, moral motivation, and strictness. The Cronbach α in the current study is 0.95.
As private regard, personal motivation and strictness scores were (i) significantly different in vegans compared to vegetarians and (ii) significant predictors of WEMWBS and PSQI, we also added diet type as additional covariate to linear regression models 13 and 14, however, diet type was not found to predict WEMWBS and PSQI (Please see Supporting Information: Table 3S).

| DISCUSSION
The aim of this preliminary study was to examine the associations between diet type, dietary identity, personality, and mental and sleep health in a sample of vegetarian and vegan participants. Overall, we found that personality traits and components of dietary identity significantly predicted both sleep and mental health. Furthermore, our results showed that complex interactions between dietary identity and personality traits predicted higher stress and worse sleep quality.

| Personality traits and mental outcomes
Our analysis showed that personality traits did not predict overall We found that higher levels of depression and anxiety were predicted by higher levels of empathy. Research studies have found that vegans and vegetarians tend to report higher levels of empathy compared to omnivores 14 which may relate to higher levels of empathic concern for the welfare of humans and animals reported for individuals who follow a plant-based dietary pattern. [44][45][46] However, it is well known that maladaptive components of empathy (such as personal distress, a maladaptive form affective empathy and interpersonal guilt, a maladaptive form of cognitive empathy 47 ) may confer risk for anxiety and depression. 25,26,47 This is even more pronounced for affective empathy as evidence from meta-analyses show that higher levels of affective empathy (an emotional response that allows an individual to perceive and experience another's emotional state), but not cognitive empathy (engagement with higher cognitive processes that allows an individual to understand the emotions of others), is associated with depression. 25 Therefore, future research should include analyses of both cognitive and affective components empathy to better understand the risk for depression in vegans and vegetarian populations.
We found that lower levels of extraversion predicted higher depression scores, in line with results reported by Hakulinen et al. 48 Yet in the research literature, associations between extraversion and diet types are not consistent (i.e., some studies report higher levels of extraversion in vegetarians and vegans compared to omnivores, 16,49,50 others report no differences 51 or higher levels of extraversion were found to be associated with meat consumption. 12,13 Additionally, research to date has shown positive associations between introversion and depression in unselected samples. 52,53 Hence, it is crucial to understand extraversion/introversion traits in relation to diet type to better understand our findings. Regardless, it is important to note that inconsistencies may be described by lower levels of the personality trait hierarchy. Domain-level traits (neuroticism, consciousness, agreeableness, extraversion, openness) predict a wider range of phenomena at a modest level, while aspect and facet-level traits (affiliation, positive affectivity, energy, and ascendence 54 ) predict a narrower range of phenomena, but with a higher degree of accuracy and strength. 55,56 Converging evidence comes from Tan et al. 16 showing that vegetarian and vegans report higher levels of energy, a facet-level trait within the extraversion domain, which may explain higher scores for extraversion overall reported for this population. Additionally, specific associations of psychopathology may exist at the lower level of the personality trait hierarchy. 57 For instance, depression is found to be associated with lack of positive affectivity 58 and low levels of positive emotionality are found to prospectively predict depression. 59 Although we cannot infer causality between low extraversion and higher levels of depression in our sample, one study found that vegetarians reported lower self-esteem, lower psychological adjustment, and more negative moods compared to omnivores. 60 This indicates that there may be associations between depression and aspect and facet-level personality traits within the extraversion domain that are specific to vegan and vegetarian populations.
For depression, we expected that neuroticism would predict higher depression scores in our sample population given that neuroticism is strongly associated with mental health disorders and risk of prospective diagnosis 19,61,62 and the association between neuroticism and depression has been reported in vegan and vegetarian populations. 17

| Dietarian identity and mental and sleep health outcomes
In terms of dietarian identity, we found that higher private regard We also showed that higher levels of stress, however, was predicted by higher levels of dietarian centrality (Model 8) and neuroticism and centrality interaction predicted higher levels of stress (Model 9). Given its socially nonnormative status, plant-based identity (compared to omnivorous identity) may be more salient and more central to one's self, therefore, this nonnormative identity (along with neuroticism) may have contributed to higher levels of stress experienced by plant-based eaters. 74,75 Regarding sleep quality, lower levels of dietarian centrality, but higher levels of personal motivation and dietary strictness (Model 11), and interactions between conscientiousness and (i) centrality, (ii) personal motivation, and (iii) strictness (Model 12) predicted lower PSQI scores (i.e., better sleep quality). As there is a bidirectional relationship between mental health and poor sleep outcomes, [76][77][78][79] our findings showing associations between higher levels of dietarian centrality and higher levels of stress in our study could be explained by this bidirectional relationship. Our findings showing associations between higher levels of personal motivation and strictness (along with higher levels of conscientiousness) and better sleep quality we believe, could be explained by positive lifestyle choices (e.g., healthy eating, physical exercise, not smoking, etc.) made by conscientiousness individuals who strictly adhere to plant-based diets for reasons related to health and well-being. For instance, compared to vegans following the diet for ethical reasons, those doing so for health reasons reported eating more fruit and fewer sweets, 80 which are known to be associated with better sleep outcomes. 81,82 Additionally, it is possible that these individuals would be involved in better sleep hygiene practices as evidenced by Duggan et al. 29

| Limitations
The current study has a number of limitations which need to be considered when interpreting the findings. First, due to the crosssectional nature of the study, we could not determine causal relationships, hence, reverse causation is also possible. Second, in the current study, nutrient intakes were measured by using a tool that processes dietary data from the FFQ. As dietary intake measures rely on the ability of participants to recall and report, underreporting may be possible. 83 Third, this study is limited to the British population, and it has been shown that diet type and mental health associations might not be associated the same way across cultures. 84 Fourth, although the effect sizes of some of the associations are small, small effects may nevertheless be socially important. 85 Fifth, it should be noted that the Cronbach's α for the BFI was rather low, however, similarly low values for the BFI were reported before 12,13,86 and this could be explained by the general weakness of the BFI and its brevity. Finally, as the current study is preliminary and skewed toward females, our findings should be replicated in bigger sexmatched samples. Therefore, future cross-cultural longitudinal studies in bigger cohorts, preferably by using objective measures (e.g., biomarkers) to assess dietary intake, as well as mental and sleep health are warranted to uncover the complex associations between diet type, personality, dietary identity, and mental and sleep health outcomes.

| CONCLUSION
The current preliminary study extended our knowledge regarding the predictors of mental and sleep health in plant-based eaters and highlighted the importance of considering dietarian identity traits, in addition to personality traits, in predicting health outcomes.

CONFLICT OF INTEREST STATEMENT
The authors declare no conflict of interest.

DATA AVAILABILITY STATEMENT
The authors confirm that the data supporting the findings of this study are available on request.

TRANSPARENCY STATEMENT
The lead author Christle Coxon affirms that this manuscript is an honest, accurate, and transparent account of the study being reported; that no important aspects of the study have been omitted; and that any discrepancies from the study as planned (and, if relevant, registered) have been explained.